Dry-expansion evaporator for ammonia refrigeration systems

Abstract

The invention relates to a dry-expansion evaporator (1) for ammonia refrigeration systems, comprising a collecting pipe (2) and a discharge pipe (3) for the refrigerant gas. The invention is characterized in that the collecting pipe (2) and the discharge pipe (3) are connected together via a siphon (5), wherein the open ends of the collecting pipe (2) and the discharge pipe (3) are arranged next to each other, and the lowest points of the refrigerant evaporator pipes (6) are incorporated into the collecting pipe (2)

Description

[0001] Dry expansion evaporators for ammonia refrigeration systems

[0002] The invention relates to a dry expansion evaporator for ammonia refrigeration systems.

[0003] Dry expansion evaporators of this type are used, for example, in refrigeration and cooling systems in warehouses, cold stores and for air conditioning.

[0004] Ammonia refrigeration systems are increasingly being used again in industry, commerce, and commerce. Ammonia as a refrigerant, known as R717, is a natural refrigerant with no direct global warming potential (GWP) and no ozone depletion potential (ODP). Therefore, various efforts are being made to increasingly use ammonia as a refrigerant to replace climate-damaging CFC refrigerants.

[0005] However, to ensure efficient operation, ammonia refrigeration systems use so-called flooded evaporators. Flooded evaporator operation results in large refrigerant charges and, in addition, requires a large amount of space for the liquid separator downstream of the evaporator.

[0006] Due to the toxic properties of ammonia and the aforementioned technical requirements, increasing efforts are being made to reduce the charge volume of the systems. This is possible, for example, when ammonia refrigeration systems are operated in so-called dry expansion mode.

[0007] In dry expansion mode, the evaporator of the ammonia refrigeration system is continuously flowed through by the two-phase refrigerant mixture. The refrigerant is completely evaporated in the refrigeration system's evaporator. The dry, gaseous refrigerant is then drawn in by the compressor and, after compression, recirculated further.

[0008] In ammonia refrigeration systems, refrigeration oil is added to the refrigerant to lubricate the moving parts of the compressor and to seal the pressure-building areas within the compressor. Furthermore, the refrigeration oil dissipates the heat generated in the lubrication gap. To ensure low-friction operation of the compressor, refrigeration oil must be continuously supplied to the compressor in the appropriate dosage and kept in circulation.

[0009] Furthermore, to defrost iced evaporators in ammonia refrigeration systems, hot gas defrosting is used to heat and melt ice in the evaporator in refrigerant-to-air refrigeration systems by reversing the refrigeration system. This makes it more difficult for the refrigerant to condense in the evaporator, and liquid condensate can accumulate in the evaporator.

[0010] However, as mentioned above, the use of so-called hot gas defrosting in the prior art is particularly disadvantageous: condensate forms in the evaporator, which accumulates in the lower part of the evaporator and remains there. This is primarily due to the collector design with its raised intake port, which sometimes results in insufficient defrosting of the iced-up evaporator.

[0011] Another disadvantage is that the refrigerant ammonia mixes relatively poorly with the refrigeration oil. In dry expansion operation of an ammonia refrigeration system, a nearly miscible oil is added to the refrigerant ammonia. The oil settles in the gas phase of the ammonia at the lowest points in the refrigeration system components.

[0012] In ammonia refrigeration systems, this effect leads to the risk of refrigeration oil accumulating at the evaporator outlet in the lowest rows of tubes. Due to the risk of liquid hammer, the accumulation of refrigeration oil in certain areas of the system should be reduced and the affected components deoiled. If this aspect is neglected, a buildup of refrigeration oil in the evaporator can lead to a surge of the liquid mixture being sucked in by the compressor. This creates the risk of flooding the compressor chamber with oil, which can lead to the destruction of the compressor due to liquid hammer.

[0013] According to EP 3 705 813 A1, it is known to prevent such liquid hammer caused by lubricants in the refrigerant circuit by using beveled suction nozzles, which only slightly influence the flow behavior in a refrigerant circuit when the oil quantity varies and the fill levels of an end of a collector pipe designed for oil separation vary. However, the design disclosed therein is not suitable for continuously tolerating widely varying liquid quantities, such as those that can occur in reverse operation for defrosting evaporators.

[0014] The object of the invention is to design an evaporator for ammonia refrigeration systems for dry expansion operation in such a way that the risk of liquid slugs for the compressor is reduced.

[0015] The problem is solved by an object having the features according to patent claim 1. Further developments are specified in the dependent patent claims.

[0016] The object of the invention is achieved in particular by a dry expansion evaporator for ammonia refrigeration systems, which, in addition to the usual evaporator components, is equipped with at least one collector tube and one outlet tube for the refrigerant gas. According to the invention, the collector tube and the outlet tube are connected to each other via a siphon and arranged side by side. This creates a preferred flow direction within the siphon. The siphon is preferably arranged at the evaporator base at the lowest point of the dry expansion evaporator.

[0017] A siphon is generally an odor- or gas-tight, yet liquid-permeable, closure for pipe systems and vessels. Its functional principle is based on an S-shaped pipe whose lower bend always remains filled with liquid, thus preventing the passage of gases, such as sewer gases. However, a siphon in refrigeration systems can also be used in a generally gas-permeable mode if it is only partially filled with liquids. According to the invention, a siphon used in this mode can be used as a buffer vessel for liquid volumes arising in different operating modes. According to the invention, it is designed to include a collecting container that can be configured independently of the flow cross-sections of connected lines.

[0018] The siphon is preferably designed as a flat, cylindrical, upright container with a flat, closed siphon base as its lower boundary. The side surface is formed by a circular-cylindrical siphon casing. The siphon cover closes the siphon at the top. Recesses for the vertical collector pipe and the vertical insertion end of the outlet pipe are arranged in the siphon cover, which penetrate the siphon cover from above.

[0019] The outlet pipe advantageously consists essentially of three sections, viewed against the flow direction: a horizontal section with a connection to the compressor's suction nozzle, an adjoining bend, and a vertical section. The vertical section has a beveled spigot at its end. With the spigot end, the outlet pipe is advantageously inserted into the siphon all the way to the siphon base. This allows the siphon base to act as a stop when the inserted outlet pipe is installed. At the same time, it ensures that the beveled end of the outlet pipe reaches into the liquid even when the liquid level in the siphon is low, optimally incorporating it into the flow circuit, which is important for continuous lubrication of moving parts.

[0020] Preferably, the insertion end of the outlet pipe in the siphon is designed as a baffle plate, with the longest part of the beveled end of the outlet pipe being arranged on the side facing away from the collector pipe. The refrigerant evaporator tubes are integrated into the collector pipe above the siphon, so that the siphon forms the lowest point of the evaporator. If the elbow is located directly above the insertion end of the outlet pipe, evaporators with a low overall height can be realized. In this context, the embodiment of the invention as a ceiling-mounted evaporator is particularly preferred.

[0021] If the base area of ​​the siphon is significantly larger than the cross-section of the outlet pipe, stable flow conditions can be achieved within the siphon, which depend only slightly on the amount of liquid in the siphon. The immersion depth of the beveled end of the outlet pipe will vary only slightly. A preferred flow direction will always be established between the collector pipe and the outlet pipe. It has been shown that, particularly for larger evaporators with power outputs above 50 kW, it is advantageous if the area of ​​the siphon base is at least four times the cross-section of the outlet pipe. Accordingly, the invention is suitable for evaporators with power outputs above 50 kW. The concept of the invention can be summarized as follows:

[0022] The accumulated refrigerant is extracted and deoiled at the lowest point of the refrigeration system's evaporator via a siphon, preventing a large accumulation of condensate and refrigeration oil. The siphon is designed to be extremely compact and space-saving compared to conventional separators in flooded evaporators. The siphon is located at the bottom of the refrigerant receiver, below the last row of tubes, and thus represents the lowest point of the evaporator, where the refrigerant and refrigeration oil collect. By design, the liquid in the evaporator flows to this point by gravity.

[0023] The intake nozzle is angled and is inserted vertically from above into the siphon and extends to the bottom of the siphon. The inserted nozzle side is angled to promote the extraction of the refrigerant and the refrigeration oil through the surface tension between the pipe and the oil. When properly aligned, the inserted pipe also acts as a baffle plate, enabling the gaseous refrigerant to be extracted from the evaporator with minimal pressure loss.

[0024] The advantages of the invention are manifold. For example, the siphon allows for complete extraction of the refrigerant and refrigeration oil from the evaporator. Defrosting times for an iced-up evaporator are significantly reduced, as the evaporator is completely drained of liquid and hot-gas defrosting can take effect immediately. Furthermore, temporary oil accumulation in the evaporator is avoided, and instead, continuous oil extraction and thus a steady oil supply to the compressor are ensured. This protects the compressor from surge-like oil intake and flooding of the compressor chamber. Further details, features, and advantages of embodiments of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. In the drawings:

[0025] Fig. 1 : Side view of dry expansion evaporator section,

[0026] Fig. 2: Perspective view of the siphon with collector pipe and outlet pipe and Fig. 3: Side view of the siphon.

[0027] Figure 1 shows a section of a dry expansion evaporator 1 of an ammonia refrigeration system in the area of ​​the evaporator base 4. The dry expansion evaporator 1 is characterized in that the collector pipe 2 for the escaping refrigerant gas and the outlet pipe 3 for connection to the intake port of the refrigeration system's compressor are fluidly connected to one another via a siphon 5. The refrigerant gas flows from the collector pipe 2 via the siphon 5 into the outlet pipe 3 and is subsequently sucked in by the refrigeration system's compressor. Liquid refrigerant, or condensate, as well as liquid refrigeration oil, flow downwards in the collector pipe 2 into the siphon 5 by gravity and is continuously entrained by the gas flow.

[0028] Siphon 5 is located at the lowest point of the dry expansion evaporator 1 to continuously suck the refrigerant oil and liquid refrigerant out of the evaporator during operation. This ensures that no liquid accumulations can form in the dry expansion evaporator 1.

[0029] Figure 2 shows a perspective view of the siphon 5 as a component of the dry expansion evaporator 1. The collector pipe 2 is arranged vertically and ends in the siphon 5, so that any condensate from the refrigerant and refrigerant oil that may form collect in the siphon 5. The outlet pipe 3 for the refrigerant vapor extends upwards from the siphon 5, through which the refrigerant-oil mixture leaves the dry expansion evaporator 1 toward the intake port of the refrigeration system's compressor.

[0030] As an example, refrigerant evaporator tubes 6 are shown, which are arranged vertically and open into the collector tube 2. The lowest refrigerant evaporator tubes 6 are arranged above the inlet of the collector tube 2 into the siphon 5.

[0031] In the perspective view, the siphon 5 is shown as a flat, cylindrical container with a diameter equal to the sum of the diameters of the collector pipe 2 and the outlet pipe 3.

[0032] Figure 3 shows the siphon 5 in detail and enlarged in a side view. The siphon 5 consists of a circular-cylindrical siphon shell 10, the flat siphon base 9, and the perforated siphon cover 11. The vertical part of the outlet pipe 3 is inserted at a beveled angle into the siphon 5 from above and extends to the siphon base 9. The lowest refrigerant evaporator pipe 6 is inserted into the collector pipe 2 above the siphon 5, so that the entire refrigerant flow is directed through the siphon 5. The refrigerant volume flow undergoes a deflection of 180° from the inlet into the siphon 5 from the collector pipe 2 to the outlet from the siphon 5 through the insertion end 7 of the outlet pipe 3. The refrigerant flow undergoes a further deflection of 90° in the area of ​​the bend 8 and leaves the outlet pipe 3 in a horizontal direction in the direction of the compressor (not shown).

[0033] List of reference symbols

[0034] 1 dry expansion evaporator

[0035] 2 collector pipe

[0036] 3 Outlet pipe

[0037] 4 Evaporator base

[0038] 5 Siphon

[0039] 6 Refrigerant evaporator tube

[0040] 7 Insertion end of outlet pipe

[0041] 8 manifolds

[0042] 9 Siphon bottom

[0043] 10 siphon casing

[0044] 11 Siphon ceiling

Claims

Patent claims 1 . Dry expansion evaporator (1) for ammonia refrigeration systems with a collector pipe (2) and an outlet pipe (3) for the refrigerant gas, characterized in that the collector pipe (2) and the outlet pipe (3) are connected to one another via a siphon (5), wherein the open ends of the collector pipe (2) and the outlet pipe (3) are arranged next to one another and the lowest points of the refrigerant evaporator pipes (6) are integrated into the collector pipe (2).

2. Dry expansion evaporator (1) according to claim 1, characterized in that the siphon (5) is arranged on the evaporator bottom (4) at the lowest point of the dry expansion evaporator (1).

3. Dry expansion evaporator (1) according to claim 1 or 2, characterized in that the siphon (5) is designed as a flat, cylindrical, upright container which has a closed siphon base (9) at the bottom and an inlet for the vertical collector pipe (2) and the vertical insertion end (7) of the outlet pipe (3) at the top.

4. Dry expansion evaporator (1) according to one of claims 1 to 3, characterized in that the outlet pipe (3) is formed from a horizontal section, a bend (8) and a vertical section, wherein the vertical section is designed as a spigot end (7) of the outlet pipe (3) in a beveled manner.

5. Dry expansion evaporator (1) according to claim 4, characterized in that the beveled end of the outlet pipe (3) is inserted into the siphon (5) up to the siphon bottom (9). Dry expansion evaporator (1) according to one of claims 1 to 5, characterized in that the insertion end (7) of the outlet pipe (3) forms a baffle plate region in the siphon (5) in that the longest part of the beveled end of the outlet pipe (3) is arranged on the side facing away from the collector pipe (2). Dry expansion evaporator (1) according to one of claims 1 to 6, characterized in that refrigerant evaporator pipes (6) are integrated into the collector pipe (2) above the siphon (5). Dry expansion evaporator (1) according to one of claims 1 to 7, characterized in that the dry expansion evaporator (1) is designed as a ceiling evaporator. Dry expansion evaporator (1) according to one of claims 1 to 8, characterized in that the siphon base (9) occupies at least four times the cross-section of the outlet pipe (3).Dry expansion evaporator (1) according to one of claims 1 to 9, characterized in that the dry expansion evaporator (1) is designed with a power above 50 kW.

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